We are studying tension-induced changes in cell shape during gastrulation in the sea urchin. Cell rearrangement in the archenteron of the sea urchin embryo is thought to occur via both active epithelial cell rearrangement and tension-induced rearrangement in response to pulling by secondary mesenchyme cells. This project will use confocal imaging of actin (stained with rhodamine phalloidin) in whole embryos to examine changes in cell shape and the actin cytoskeleton associated with the rearrangement that occur during gastrulation. In addition we will be using the multiphoton microscope to image morphogenetic movements of cells in the archenteron during gastrulation. Either individual cells will be labeled with DiI or the plasma membranes of all cells in the embryo will be labeled with FM 4-64. Zseries through the developing archenteron will be collected in timelapse. These data sets will either be viewed using the 4-dimensional viewer program developed by the IMR or the data will be used to create 3D reconstructions at various timepoints.